Concentration of aliphatic acids



Patented Sept. 14, 1943 I I r: I 7 v 1 CO EN I N intr cac es il i 4 II I I Henry Dr,eyfu s, London, and lwalter Hen'ry I Groombridgeyspondon,"near Derby, Englandg assignors to'Celanese' Corporation" ofiAmerica,

' I No Drawing; Application "April 21,1 1942'; serial 5: a 43 ,930.11; Grcat Britain lvreyzcia r I I I I I I I I II 10 Claims; (Cl. 260 ,230)- A i I This invention relates'to therecoveryoilower I 1 soc ates; above, .it .is" preferred that the iatty acids particularly acetic acid. It islespe metalifsalt used should, be'a'n1 alkali metal .sul-, clallyconcerned withtherecovery of s uchacids, pirateTahdgthcei lifition will ndw'lbe described together with cellulose esters, vfrom solutions of I more particularly with reference" to v the procelluloseesters in the said acids; e. g. the re- 5 cedureliwhich caribeadopted when such a salt is very of cellulose acetate an d aeet Iacidafriom used; I 4 I I solution's'otcellulose acetate in acetic acid, for {Lill e allgaliinltal,il p abe d be pre 1 example the solutions obtained'by th acetylainsubstantialproportion, "e; g. tothe extent of tion of cellulose with aceticY anhydride in the from '3 to 1037 or more based o'n ithe" water vpresence of sulphuric acid. 'I 'heinventionwill 1Q present. lilteisrpreferred. to'use an amount of be described more -particularly, with reference to alkali inetall'su lph'ate sufilcient to saturate the theitreatment of sucrnsolutions; aqueous aceticl'acid/ i i I vI I I As', regards the extraction of acetic acid from tate and recovering acetic acid in concentrated I he aqueous liquid; containing acetic acidand form from solutionstorpcellulose acetate in acetic a ali; met l. su ph e'th a ecarri O t acid, is to precipitate the cellulosezacetateby asl tq l v fi vthe" l r t ofi' th action, of an aqueous liquidand then, after. acid p'r sehtbef xt ac separating the precipitated celluloseacetate, to A n a dy v n n w pr cess is of Acommonmeth d; of 1501 ting cellulose acextract acetic acid from the, residual aqueous especial valuefor the isolationof cellulose 'a'celiquid by means of asolvent for acetic acids 2Q tate irom-; acetylation l.solutions obtained by i It has been foundthat 1111511011 processesrthe a ylfilfi 6 1 h: c ti nhi ri i proportion oft solv ent foracetic acid which need acetic acid in presence of sulphuric acid. When be employed'in relationto the amount, of a id applying -thefl-process, to such solutions (which recovered can bereduced very greatly if the m y av 2 enc .f e" Sulphuric 301d aqueous I acid undergoing extraction contains a content is iconvrtedto alkali metal sulphate by metal salt; preferably an alkali metal sulphate neutralisatio (O f pa tial eufi isfl bn i (which expression .isused to includeanvalkali bisu phate-is to be used). W J p a metal bisulphate) and if the extraction of, the alka metaL-"v-h dmxid icarbonate or i acetate I acetic acid is discontinued when a substantial which'can be'addeddirectly tothecellulose aceproportion thereofjstill remains in th aqueous @Qtate solution or included in thepprecipitation q id f .v i i Y J liquid, By usingjalkaliemetal -hydroxide, car- Ac cording ,-to, the present inv'ention cellulose bon acet eio n l r sa f the S1117 acetate-is precipitatedirom a solution thereof in p ri i d he o ma ionc n de i of acetic acid by the action .of anaqueous solution I salts other than alkali; metal sulphate, qrof acids or a metal saltcontaining some: acetic acid and, 5 3 others-than acetic acid, inthe liquidto be eX- after separatingthe precipitated cellulose ace; tracted zor that to be used for precipitation of tate,-,a*p art only oithe' acetic acid isextracted celluloseacetate; 7 i I I from-theaqueousliquid by the action ofa solvent When. cellulose acetate-;,solution s containing for; acetic; acid, "at ,least' parttiof the vresidual sulphuri c re' e de r cd OY h aqueous liquid being then-used'for theipreciplta -i' 10 quantity of alkali metal sulphate present will ir -icrease with each cycle of; operations; unless ,a acid solution thereof. J .1 i t a suitable proportion is removed from timetotime .iT p t i o aipart. only of the acetic andpreferablyat each-cycle. This, can be do ne acid content-of the aqueous liquid, combined with by effecting-substantially complete extraction 1 the presence, of the metal salh enablesthe acetic {1? of'the acetic acid .trom-aportion of .the dilute tion of, further cellulose, acetateifrom 'an acetic acid of the cellulose acetatesolution to ibe=reacidcontaining the amount of the salt which it covered by extraction withasproportionofysolis desired toremove. The completely extracted ventwhichls,very-much-1less than isthe .case' liquorcan, then be runto; waste aftersolvent when these expedient's are not employed. rAt-the 3 recovery: A-n alternative-procedure istto allow v same time at least part of the metal salt con-e 5 0 some-otithesalt to crystallise'out, preferably by tentof theliquld, after'extraction ofacetic acid cooling; and remove it ;by filtration. Again, it is from-the latter, is utilised ina-succeedingopera- I I possible to regenerate alkalimetalhydroxide or tion without expensive operations sllch aig'cpn acetateinvtheliquorsvand at theisametimerecentration of themetal salt or isolation f the move part 0r .;a1l af -the accumulation of sulor} phate ion by t'reatin theiliduors, after partial or complete extraction, with an oxide, hydroxide or acetate of a metal which forms an insoluble sulphate e. g. with calcium acetate. The precipitated sulphate can then be removed and the regenerated alkali metal hydroxide or acetate is available for combining with the sulphuric acid of a cellulose acetate solution containing this acid, as described above. The first mentioned procedure is, however, preferred in that it afj fords an opportunity of removing waterirom the cycle and thus compensating for freshwater introduced into the cycle for -washing and/or precipitation of the cellulosegacetateg 'Yin the case where complete extraction-iof'a'qpart of the,-:; waste liquor is practised, this is advantageously. performed with fresh, solvent, which his ..then passed on and utilised for Ypartial extraction;

of the bulk of the aqueous acid." The part sub jected to complete extraction can be a:pcr'tion.of:

the partially extracted liquor so obtained.

.Ifhe, alkali metal sulphatesolutionffrorn which content. The acetic .a'cidcontent of 'the alka i.

metal sulphate solution is therebyincreased and it is thereaftenused to precipitatefcelluloseacetate from solution The precipitated cellulose acetate after the washing: with thefalkali metal sulphate solution is'w'a'shjd with'water, the washin'gs being '.mixe d with 'th 'e alkali metal sulpha'te solution before the latter --is used "for Washing cellulose acetate j'as 'mentioned iabo water isthereby'introdu'ced at eachryc i oper- An exampleof a suitable solvent having a boiling point above that of acetic acid is amyl acetate.

When acid sulphates, for example, sodium bisulphate, are present in the aqueous acetic acid, the use of solvents containing esters, e. g. ethyl acetate, iis undesirable owing to the-danger of hydrolysis. Inisuch a case, it is convenient to use as solvent an ether.

The extraction with the solvent is advantageously effected systematically, a given body of solvent being used to extract successively a. series if acidsolutions of,progressively increasing con- Batch'methods may be used, extrac in being ,then'eenveniently effected in a series 10f lvessels rand 'Ihfi :extract and extracted liquor being transferred, from vessel to vessel, the ex- -'tra ct :for.:-extraction of further acid of higher "conc'entration'than that just extracted, and the extracted-liquor for extraction by solvent containing a smaller proportion of acid than that just used jror' extractlon. f A'g'ain,-continuous counterflow extraction may be used,the= solvent "being run in -counter '-fcurrent to the aqueous liquor, i "The "apparatus mayithen conveniently takefthe "f'orm'of a column, through which-the aqiieous acid and solvent, are passed in} counteiflow, whichever has the lower specific gravity-being in'trdduced at'the lower partof: the column. The liquids -a re adv anta'gcously introduced into the column-in; a'series of fine streams so as to provide a large "surface of contact be tween the liquids. fFurther the-columnmaybe provided with suitable packingrnaterialto the same end. a

ations andfc'anfbe arranged tofcompeiisalteffor that :rem-oved, as described abovefin the form of completely extracted *alkalijfrnetal sulphate solution ff f) When counter-current washing of '-the precipi-' tated cellulose acetate and final-washing with waterris practised, the "partiallyextracteddilute acid :is conveniently mixed with; the --'washing liquors resulting frdm the-washing with water at a stage-where the concentration of faceticf acid in said WashingliquorsflPP oxiinates to that of the'tlilute'acid; -various solvents may be use'df ior the extraotion. 'Theyshould preferably lee srael; as do r-i'ot dissolve in, or take 'up v'vater' from,aqueous-alkali metal sulphate solutions to' a very substantial extent. Their-boiling points may be "a'lzvove -or below that of the acetic acid to' be extracted. Further, their boiling points should preferably differirom that-of-the aee'tic acil'fby sornuch that {they can be readily separated from tlie acid by a distillation pera'tion, They may' consist of single chemical compeunds for mixtures :of t' om'po ndswi Examples 5 of solvents-suitable m the extra'ction of acetic agfld and-' having "a-boil'ing point below that of cetic'iacid are :diethyl ether,- di-' propy-l ether; isopropy l ether, ethyl acetate and similar volatile esters of :aceticiacid,=methyl- Gene-chloride and'ethylene chloride. Particular mention may be r'n'ade' of themixtures of solvents for acetic-acid with hydrocarbons,mentioned in U. Pa'tent No. 1 ,696,482 A-suitable mixture is that of filethyll ether with petroleum ether 01 ethyl "acetate with benzenf-el 'gf. a mixture o'f parts by volume offpbhyl acetate with 6: 5;- parts byvolume-ofben'zene. i

' iIsolation dteoncehtrtitdacid from the extract can' 'be :eifected' by distillation. ili he extract can be idistilled Fb'atches I or continuous-stills can be used "Fherecovered solvent can of course be :return'e'd {t the extraction appariat tu's. iii/hen the solvent's usedas extractants form with water azeotropic' =mixtures of minimum boiling 'point, water! extracte'd' w it h the acid to be concentrated can be removed to a' substa'nti al deg'ree during the distillation, in the form of such a m'ixture, together :with ithe 'solven'tflthereby facilitating theiproduction o'f a highly zconceritratedor-even substantiallyianliydrousLacid. I The process of the invention' 'can'zalso berapplied :to :the" isolation of cellulose esters from solutions generallyiin lower Efatty acids, particularly solutions which have been prepared"by I esterification :ofrcllulose in presence era lower I lyst 1a suitableisalt :is sodium phosp'ha'te; The

phosphate :can .besfo'rmed in s'itu as in the case ofithe sulphate, :byadding a' hydroxidegcai bon'ate or lower fatty a'cid i salt, corresponding to the low er. :ratty acid- 111 the iesterlfication mixture, to the icellulose-"zesteri solution; or the precipitation liquid: :.1'n :IOIldr itto combine with the phosphoric acid, 1 i 1 Having described our invention iwhat :welrdesire to secur'e b'yLetters Patent 'isi' 1' 1. Process for-the recovery 'of cellulose acetate and acetic acid frem a 1 so'lut-i-en of cellulose e: tate in acetic acid, which comprises-precipitating .action of an aqueous solution accepts the cellulose acetatefrom-"the solutionuby the action of an. aqueous solution bfza metallfsalmcon staining some acetic acid,.-the1metal:.saltamounts ing to at least 3% based on thewater: present,

separating the precipitated cellulose acl'tate (ex;

the solution by the action of an aqueous solutionof a metal salt containing some of the lower fatty acid, the metal salt amounting to at least 3% based on the waterpresent, separating the V precipitated cellulose ester, extracting part only of the'lower fatty acid from; the aqueous liquid by the action of a solvent for the lower'fatty acid and using at least part of the residual aqueous liquid for the precipitation of further cellulose ester from a lower fatty acid solution thereof.

3. Process for the recoveryof cellulose acetate and acetic acid from a solution of cellulose acetate in acetic acid, which comprises precipitating the cellulose acetate from the solution by the action of an aqueous solution of a metal sulphate containing some acetic acid, the metal sulphate amounting to at least 3% based on the water present, separating the precipitated cellulose acetate, extracting part only of the acetic acid from the aqueous liquid bythe action of a solvent for ,7

' acetic acid, and using at least part of the residual aqueous liquid for the precipitation of further cellulose acetate from an acetic acid solution thereof.

4. Process for the recovery of cellulose acetate and acetic acid from a solution of cellulose. acetate in acetic acid, which comprises precipitating the cellulose acetate from the solution by the of an alkali metal sulphate containing some aceticacid, the alkali metal sulphate amounting to at least 3% based on the water present, separating the precipitated cellulose acetate, extracting part only of the acetic acid from theaqueous liquid by the action of a solvent for acetic acid, and using at least part of the residual aqueous liquid for .the precipitation of further cellulose acetate from'ani acetic acid solution thereof.

5. Process for the recovery of a lower fatty acid and a cellulose ester of a lower fatty acid from an esterification solution of the said ester made by esterification of cellulose with a lower fatty acid anhydride in a lower fatty acid usingsulphuric acid as catalyst, which comprises converting the sulphuric acid to a metal sulphate, precipitating the cellulose ester from the'solution by the action of an aqueous solution of the metal sulphate containing some of the lower.

fatty acid so that the resulting aqueous liquid contains at least 3% of the metal sulphate based on the water present, separating the precipitated ester, extracting a part only of the lower fatty.

acid from the aqueous liquid by the action of a solvent therefor, removing the solvent from the extract and using the residual aqueous liquid as at least'part of an aqueous liquid for. the precipitation of further cellulose esterfrom a solution thereof in the lower fattyacid.

6. Process forthe recovery of cellulose acetate and acetic acid from an acetylation solution made :by .acetylatingxcellulose aceticfanhydride in acetic; acidiusinglsulphuric acid as catal y-st, which icomprises converting?lthe' sulphuric': acid intoso- Adium: sulphate; precipitating theicellulose acetate from the solution by the action of an": aqueous solution ofissodium" I sulphate containing some acetic; 5 acid so that the-J resulting: faqueo'us liquid containsamass-3% of sodium sulphate based on the water. present, separating the precipitated cellulose acetate, extracting a part only of the acetic acid from th aqueous liquid by the action of a solvent for the acetic acid, removing the solvent'from the extract and using the residual aqueous liquid as at least'partof .an aqueous liquid for the precipitation of further cellulose L acetate from an acetic acidsolution thereof.

'7. Process for the recovery of cellulose acetate and acetic acid from an acetylation solution made by' acetylating cellulose with acetic anhydride in acetic acid, using sulphuric acid as catalyst, which comprises precipitating the cellulose acetate'from the solution by the action ofan aqueous solution of sodium sulphate containing some acetic acid and sufiicient sodium acetate to convert the sulphuric acid into sodium sulphate so that the aqueous liquid contains at least 3% of sodium sul- .phate based on the water present, separating the precipitated cellulose acetate, extracting a part only of the acetic acid from the'aqueous liquid by the action of a solvent for the acetic acid, removing the solvent from the extract and using the residual aqueous liquid as at least part of an aqueous liquid for the precipitation of further" cellulose acetate from an acetic acid solution thereof.

8. Process for the recoveryof cellulose acetate and acetic acid from an acetylation solution made by acetylating cellulose with acetic anhydride in acetic acid using sulphuric acid as catalyst, which comprises precipitating the cellulose acetate from the solution by the action of an aqueous solution of sodium sulphate containing some acetic acid and sufiicient sodium acetate to convert the sulphuric acid into sodium sulphate so that the resultant aqueous liquid is substantially saturated with sodium sulphate, separating the precipitated cellulose acetate, extracting a part only of the acetic acid' from the aqueous liquid by the action of a solvent for the acetic acid, removing the solvent from the extract and using the residual aqueous liquid as at least part of an aqueous liquid for the precipitation of further cellulose acetate from an acetic acid solution thereof.

9. Process for the recovery of celluloseacetate and acetic acid from an acetylation solution made by acetylating cellulose with acetic anhydride in acetic acid using sulphuric acid as catalyst, which comprises precipitating the cellulose acetate from the solution by the action of an aqueous solution of sodium sulphate containing some acetic acid the solvent from the extract and using the resid- ,ual aqueous liquid as at least part of an aqueous liquid for the precipitation of further cellulose acetatefrom an acetic acid solution thereof.

10.,Processfor the recovery of cellulose acetate and acetic acid from an acetylation solution made by acetylating cellulose with acetic anhydride in acetic acid using Sulphuric-acid as catalyst, which. 

